Optimization of Processing Technology of Burdock Tea and Antioxidant Activity of Its Polysaccharides in Vitro

The purpose of this study was to optimize the processing technology of burdock tea,improve the quality of burdock tea,and study the antioxidant activity of polysaccharides in vitro. Microwave-vacuum drying was used to prepare burdock tea. The preheating temperature,vacuum degree,drying temperature and slice thickness were determined by single factor experiment and response surface methodology. The polysaccharide in burdock tea was extracted by water extraction and alcohol precipitation,and its content was determined by phenol-sulfuric acid method. The polysaccharide was characterized by infrared spectroscopy and their monosaccharide composition was determined by HPLC after deproteinization,dialysis and decolorization. The scavenging capacities of polysaccharide on DPPH·,ABTS⁺· and ·OH were detected in vitro. The results showed that the highest content of burdock tea polysaccharide was 51.08 mg/g under the conditions of preheating temperature 75 ℃,vacuum degree 0.07 MPa,drying temperature 66 ℃ and slice thickness 3 mm. The water content of burdock tea was 7.85% and the rehydration ratio was 5.46 g/g. Electron microscope showed that burdock tea had a compact and uniform structure and good sensory quality. Infrared spectrum showed that burdock tea polysaccharide had characteristic absorption peaks of typical polysaccharide. The total polysaccharide content of burdock tea increased 1.6 times higher than that of burdock root. In monosaccharide component the glucose content of burdock tea increased 135 times,and the mannose content increased 7 times higher than that of burdock root. The semi-inhibitory concentrations(IC₅₀)of DPPH·,ABTS⁺· and ·OH from burdock tea polysaccharide were 1.115,1.556 and 1.047 mg/mL,respectively. The burdock tea polysaccharide had good antioxidant activity in vitro with over 65% scavenging rates.